Our hypothesis is that substances routinely found in food, specifically indoles, products of combustion and flavenoids, are inducers of an important drug-metabolizing enzyme (termed CYP3A4) that is abundant in human small intestine. To test this hypothesis, normal volunteers will be placed on isocaloric diets containing cruciferous vegetables (indoles), charcoal broiled beef (combustion byproducts) or grapefruit juice (flavenoids) after a four-day "wash out" diet. The patients will undergo endoscopic biopsy of the small bowel and sigmoid colon mucosa before and after being on these diets for seven days.